Effect of Precipitation Hardening on Microhardness and Compressive Strength of Air-Casted Dilute Mg-0.4Al-0.6Ca Alloy

Development of low-cost, rare-earth-free and high-strength magnesium alloys is highly desirable. Reduced quantity of secondary phases in dilute alloys could enhance their ductility. Dilute Mg-0.4Al-0.6Ca (wt.%) alloy with Ca/Al ratio of 1.5 was successfully air casted thanks to minor Calcium addition. The alloy showed high age hardening response, with an increment of about 36 HV in the peak-aged state. The ultimate compressive strength of as-cast and peak-aged alloys are 243 MPa and 293 MPa, respectively. Microstructural study of alloys by scanning electron microscope and energy-dispersive X-ray spectroscopy shows the formation of Mg17Al12 phase has been suppressed due to high Ca/Al ratio and Mg2Ca is the only present second phase. Microstructural comparison of as-cast, solution-treated and peak-aged alloys do not show any significant difference. This verifies previous studies that attributed the high hardness of peak-aged dilute alloys to the presence of fine plate-like Guinier-Preston (GP) zones on the basal plane.

Keywords:

Magnesium alloys , Precipitation hardening , Guinier-Preston zones , Peak-aged , Ca/Al ratio